This is the third year of a project originally approved for three years. The major objectives of the research are (1) to make accurate quantitative determinations of the rheologic properties of blood cells, (2) to relate these properties to the molecular constituents and ultrastructure of membrane and cytoplasm, (3) to examine the influence of particular pharmacologic, physiologic and pathophysiologic factors on cell deformability, ultrastructure and function. The experimental method consists in the exposure of suspended cells to well defined and controlled distortional flow fields (pure shear, pure elongation) and recording their motion, deformation and, in the case of platelets, shear-induced release.